The project is to study the hearing mechanisms and capabilities of fishes. Investigations will be conducted to determine the contribution of the swim bladder and Weberian ossicles in hearing and to determine how the different portions of the inner ear work in signal detection and processing. Experiments will be conducted to determine the response of different types of swim bladders (multi-chambered, swim bladders with positive and ambient pressure, swim bladders with multiple projections) using a probe microphone to record from inside of the swim bladder of intact animals. Additional experiments will be done using electrophysiological techniques to record from the inner ear and brain. We will determine the role of the inner ear in signal processing and also investigate the contributions of the swim bladder and Weberian ossicles to hearing by comparing signals in the inner ear when the other structures are intact and when they are altered or removed. Behavioral experiments will be conducted using avoidance conditioning procedures to determine the auditory capacities of many species of fish. Audiograms will be determined for taxonomically related species to determine correlations between morphology of auditory structures and hearing capabilities of fish. Experiments for pulse tone thresholds conducted previously on the goldfish will be extended to fishes without the Weberian ossicles.